EPDM failure causes anaerobic digester explosion

EPDM failure causes anaerobic digester explosion
The basic process flow and potential outputs from an anaerobic digestion project. (Photos courtesy of RES)

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The chances of an anaerobic digester exploding are slim to none. But that’s exactly what happened at Tim Bielenberg’s Oak Lea Farm in Aumsville, Ore. “I don’t think you could ever make it happen again,” says Alan Tank, founder and CEO of Revolution Energy Solutions (RES), the company that owns and operates the digester. “We know what component failed, but we don’t know exactly what the ignition source was. What we believe it to have been was static electricity.”

RES worked with Bielenberg over the past two years to commission the low-temperature anaerobic digester that processes up to 30,000 gallons of manure per day to create methane gas, which fuels generators and produces electricity. The process generates 190 kW of electricity, which translates to approximately 1.5 million kWh annually delivered to the grid.

Perfect combination

The explosion was more of a fluke and both tanks were back online within two weeks. RES uses an EPDM (ethylene propylene diene monomer rubber) inflatable membrane material for headspace gas storage on the tanks. “We accumulate the biogas there and then we pull it off of that headspace to consume it in the engine. For whatever reason, that EPDM failed. When the EPDM failed, the biogas that had accumulated escaped.

“The gas that was in that headspace combusted rather than going down the gas train to the engine or any other location. During that process, you have to have the exact combination of ambient air and methane for it to be combustible. It came in contact with some ignition source.”

Fortunately, the system operated as designed so it began to shut itself down after the dramatic change in gas pressure and flame aerators on the biogas train also proved effective. The minor damage was only above the rim of both tanks, and no one was hurt in the explosion. While the chances of this happening again are rare, RES has taken steps to prevent  “There are tremendous ground fields around the engine and the interconnection,” says Tank. “We ground the tanks, and we now apply a ground application to the EPDM as well.”

Moving forward

RES currently only focuses on agricultural projects, but Tank says its digester technology can be used for municipal wastewater treatment. “We are entertaining some non-farm applications right now,” he says. “We have an exclusive license for some anaerobic digestion technology that we think is uniquely suited for non-farm applications because of its tolerance to certain toxicity issues and organic loading requirements and temperature requirements.

“The anaerobic digestion technology we use can handle very high loads of nitrogen or ammonia and can operate at relatively low temperatures (i.e. 75 to 79 degrees F). Most digesters have a maximum tolerance of 2,500 mg/L of ammonia and we’re four and five times that so it starts to make applicability in non-agricultural sectors very attractive.”

RES is using the explosion at Bielenberg’s farm as a learning experience and moving forward, says Tank. “There are a lot of waste sources, whether it be manure or industrial or municipal,” he says. “The bottom line is this technology works and it works extremely well. These biomass projects will just gain more and more foothold in the United States as we continue to move forward because it allows you to take those waste streams that are very prevalent and turn them into a useful source.”


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